Differential Accumulation Patterns of Seed Proteins in Salt-Tolerant and Salt-Sensitive Rice Lines under Varying Salinity Levels

Salt-induced changes in the accumulation pattern of seed proteins were studied in salt-sensitive (MI-48) and tolerant (CSR-10) rice lines. An increase in seed protein content was observed with progress in seed development from 4 to 12 Days After Flowering (DAF) and up to maturity at each salinity level (4, 7, and 10 dS m(-1)). However, a 10-21, and 14-30% reduction in seed protein was noted when compared at a given developmental stage at all the salinity levels in 'CSR-10' and 'MI-48,' respectively. Among the four seed protein fractions, the proportion of glutelins revealed an increase (5-9%) in mature seeds of 'CSR-10' with a decrease (11-13%) in 'MI-48' under increasing salinity levels. Prolamins exhibited a reverse trend in both lines. Albumins and globulins revealed a decreased proportion in 'CSR-10' but an increase in 'MI-48' only at 10 dS m(-1) at a given developmental stage. In 'CSR-10', the accumulation pattern of the glutelin [Molecular weight (Mr.) 36-40.5 and 19-21.5 kDa] and prolamin (13 kDa) polypeptides was seen similar at the control, 4, and 7 dS m(-1) except for the higher concentration of these at later two. At 10 dSm(-1), a contradictory pattern of accumulation of these polypeptides was observed. In 'MI-48', a completely different trend (earlier and faster accumulation) of the above-mentioned polypeptides was seen at 4 and 7 dS m(-1) in comparison to the control from early stages. Prolamin polypeptide (13 kDa) showed a continuous decrease in its concentration at all the salinity levels; more pronounced at 10 dSm(-1) . Therefore, both lines revealed a different mechanism in response to a given salinity condition.